Intro to the Federal Rules of Evidence - 40

2. Non-Convicted Bad Acts on X-X (FRE 608(b))

a. Probative of truthfulness/untruthfulness
A prior unconvicted bad act may come in only if it expressly bears on truthfulness.

b. Method
A prior bad act may be proved only through cross-examination, not through other extrinsic evidence (e.g., a second witness, documents). In other words, the cross-examiner must take the witness’ answer.

c. Self-incrimination
Where the accused takes the stand in his own defense and speaks on direct only about the present crime, as a constitutional matter, the accused does not waiver his right to claim the privilege when asked about prior bad acts that have nothing directly to do with the present charged offense and are relevant only to credibility.

d. Discretion of the judge
The court weighs the probative value of the evidence against the prejudice that results to the opposing party. The exercise of this discretion will rarely be reversed on appeal.